What modifications could l do to push up the efficiency of this car?
it is an automatic rj20 twin turbo, l really just like the car. l do not need the amount of power its already got

good way to start is with a good performance exhaust and a better air filter like a K&N high performance air filter. also a better spark plug will help something like a bosch platinum which is a very nice spark plug.

Change all ur fluids to lighter ones help(if u dont live in a hot area with high temps). This will help get some efficiency out of it, also get a more efficient air-filter, K&N or similar. They r expensive at first, but can be cleaned & used over & over. Change ur plugs, but DO NOT use anything other than OEM replacements, which should be NGK Plugs. Subarus do not like Bosch, or any other plugs for that matter. Changing ur fuel filters & cleaning ur injectors should help as well. Also make sure ur tires r properly inflated. And pull anything thats heavy & u dont use out of ur car!

These r all pretty general tips for increasing efficiency that can be used on any car really. Subys can just be picky about some things.

Performance mods generally cost u MPG. The #1 thing u can do to increase efficiency is lift ur right foot. If u press less on the gas pedel, u will use less gas (shocking l know). You could also reflash to lower ur boost, but this is just using the computer ECU to do the same thing u could do with ur foot. Tape a block of wood to the bottom of ur gas pedel if u have trouble controling yourself.

Also, lighten ur car as much as possible (remove the junk from the trunk), inflate ur tires properly, & get a tuneup.